But a New York-based study has proven no difference in temperature between men wearing boxers and men wearing other underpants.

Dr Chris Love says this means changing the advice given to patients with fertility problems. "We thought the temperature of the scrotum must go up with tight underwear and we know that high temperature's bad for sperm," Dr Love said.

"This is saying that the temperature of the scrotum doesn't change no matter what type of underwear; so it's fairly irrelevant and probably not something we need to really talk to patients about as much as we thought we did."